Aerobic and anaerobic integrated treatment using microbial biofilm to improve the quality of the paper mills effluent: A reactor-based study

The pulp and paper mills significantly contribute to water pollution due to the large quantities of hazardous effluent generated during paper production. The effluent is highly concentrated and contains high levels of chemical oxygen demand (COD), biochemical oxygen demand (BOD), chlorinated compounds, color, suspended materials, lignin, and their derivatives. To address the issue of effluent treatment, the present study investigated the effectiveness of biological treatment to degrade the pollutants of paper mill effluent. We screened seven fungi and four actinomycetes for hydrolase enzymes and used a metagenomics study to taxonomically and functionally characterize the anaerobic biofilm originating from cattle rumen fluid. Based on the COD removal efficiency of the primary single-stage treatment, we implemented two- and three-stage treatments in batch process. The first step in an integrated approach using batch reactors was an anaerobic reactor to break down primary pollutants in a packed bed anaerobic reactor (PBAR), which greatly reduced COD. This was followed by aerobic treatment with actinomycetes biofilm in a sequential bed reactor (SBR), and finally, fungal biofilm treatment in a moving bed biofilm reactor (MBBR) in batch process. The effectiveness of each stage was assessed by measuring the reduction of COD. Single-stage fungal, actinomycetes, and anaerobic biofilm treatment removed 94.09 %, 95.30 %, and 95.91 % COD, respectively, from an 11,500 mg/L initial concentration within 168 h. Kinetic analysis demonstrated that the Grau second-order model accurately described COD removal across all three-reactor treatment. Two-stage fungal-actinomycetes and fungal-anaerobic treatments reduced COD by 99.82 % and 98.76 %, respectively, from a 23,500 mg/L initial concentration within 72 h while also improving other relevant parameters. An integrated anaerobic-actinomycetes-fungal treatment process effectively removed 98.86 % COD, 99.23 % BOD, 92.16 % lignin, and 94.02 % color from a high-strength effluent within 168 h. After the treatment process, the effluent meets the standard given by regulatory agencies and can be discharged into the environment without any risks. The study demonstrated that industries can implement the method to provide sustainable solutions for low- to high-strength effluents. Based on the COD levels of the effluent, the study gives industries the option to implement single, two, or three-stage treatments. The integrated approach proved to be a cost-effective and eco-friendly solution for pulp and paper mill effluent treatment, demonstrating potential for large-scale industrial applications.